Hormesis as a Particular Type of Plant Stress Response

Plants are continuously exposed to various abiotic and biotic stress factors, which influence their growth, productivity, and ecological fitness. This paper clarifies the concept of hormesis as a distinct low-dose stress response to toxic substances and presents its relationships with other plant stress phenomena. Based on evidence from the published literature, hormesis can be considered a particular type of acclimation because it involves temporary, non-heritable physiological adjustments to mild toxic stress. It is induced by low doses of toxic substances (e.g., cadmium (Cd), lead (Pb), and chromium (Cr)) and characterised by stimulated growth resulting from the moderate activation of defence mechanisms, including antioxidant activity, reactive oxygen species regulation and/or enhanced photosynthetic efficiency, as well as increased auxin content. We propose that the fundamental parameter for identifying hormetic responses should be plant growth, expressed as shoot biomass or elongation, as analyses of single physiological traits alone are insufficient. Furthermore, growth stimulation caused by factors with physiological functions (physiological factors) such as light, temperature or mineral nutrients should be regarded as forms of acclimation rather than hormesis. These assumptions provide a clearer framework for future studies on plant stress physiology.